This longitudinal study examined growth patterns of written syntactic complexity of Turkish learners of English. Using a nonexperimental corpus of 852 writing samples by 284 English as a foreign language (EFL) learners over three semesters, the study addressed the following questions: which indices of syntactic complexity characterize the writing of EFL learners most saliently at elementary, pre-intermediate, and intermediate levels? How do levels of the indices of syntactic complexity change over time as learners progress from elementary to pre-intermediate and intermediate levels? Results suggested that lower proficiency level (levels 1 and 2) writers produced similar patterns of written syntactic complexity (reliance on phrasal coordination), while at proficiency level 3, they demonstrated constructions that were more complex and of greater variety. Findings revealed that over time, learners experienced significant syntactic changes in multiple aspects of complexity; however, these changes were not necessarily straightforward or incremental across the three levels. These findings underscore issues of unpredictability and linearity in second language acquisition, while also cautioning us about the role of intensity of classroom instruction in L2 development.